(1) Field of the Invention
This invention relates high speed photography, and to a circuit for triggering a video camera located between two sensors. More specifically, the video camera is triggered by a projectile passing through a break screen on an underwater range.
(2) Description of the Prior Art
The Adaptable High Speed Underwater Munition (AHSUM) project needed a method to obtain video images of underwater projectiles during the course of their test series. Prior to this time, there was no satisfactory means of obtaining the video images that were needed, nor was there a device applicable to a variety of conditions.
The following patents, for example, disclose various types of video photography, including underwater photography and circuits in connection therewith, but do not disclose a device for controlling an underwater video camera for the purpose of taking underwater video of a high speed projectile.                U.S. Pat. No. 4,335,944 to Marshall;        U.S. Pat. No. 4,418,999 to Baxter;        U.S. Pat. No. 4,447,896 to Rines;        U.S. Pat. No. 4,713,686 to Ozaki et al.; and        U.S. Pat. No. 4,970,597 to Shepard.        
Specifically, the patent to Marshall discloses improvements in underwater elapsed time strobe-camera apparatus and the like involving sonar-triggering by a sonar beam generated co-axially with and about the camera lens axis and, as a result of novel circuits, size-reduction and packaging, adaptability for portability, with ancillary novel features of automatic predetermination of number of pictures and indication thereof.
Baxter discloses a synchronizing circuit which enables a desired phenomena to occur, such as the discharge of a flash illuminating means at a precise point along the path of travel of an article irrespective of the speed of the article in that path. The circuit utilizes two spaced sensors upstream of the precise point. The sensors are operable to detect the passage of the article and each sensor is connected to respective counter. When sensor detects the passage of the article it starts its respective counter counting in one direction at one particular counting rate. When the second sensor detects the passage of the article it causes its respective counter to count in the opposite direction from the value of the count in the first count at a different but faster counting rate. The circuit includes gate means which determine when the count has returned to a predetermined count to then cause said phenomena to occur.
The patent to Rines is concerned with problems of energy conservation and more effective utilization at desired critical times only in, for example, sonar-triggered underwater elapsed time strobe photography of objects or scenes or in applications having similar problems; and accomplishing such and other ends by restricting optical and sonar monitoring to relatively low periodicity intervals until the desired object has come within range, whereupon the apparatus automatically changes mode to take rapid successive strobe photographs or other records supplemented by contemporaneous sonar recording.
The patent to Ozaki et al. discloses a high speed, instantaneous multi-image recorder having a video camera, sensor unit and light projector. A frame memory is connected to the video camera, a flash tube is joined to the light projector, and a retarder is joined to the sensor unit. The flash tube is connected to the retarder, and a monitor is connected to the frame memory. The video camera, sensor unit and light projector are directed toward a moving object which is, for example, a golf club. When the golfer swings the club, the sensor unit detects the club, the light projector flashes, and the video camera picks up the golf ball and club head at the moment of impact. Thus, the video camera catches many instantaneous poses within a frame. Many such images picked up in a signal frame of the video camera are displayed on the monitor screen for analysis.
Shepard discloses a method of imaging a high speed event. A multiplicity of frames, or image fields, are output from a camera which scans repeated occurrences of the event. Selected data representing individual portions of frames are accumulated in essentially random order. The selected data are used to construct a composite image of the high speed event.
It should be understood that the present invention would in fact enhance the functionality of the above patents by providing a control device for an underwater video camera and triggering the underwater video camera at the precise time necessary for acquiring desired video frames, particularly in a test environment.